Using Aeroelastic Modes for Nonlinear Panel Flutter At Arbitrary Supersonic Yawed Angle

Abstract

It is commonly accepted that six in vacuo natural modes are needed for converged, limit-cycle oscillations of isotropic rectangular plates exposed to supersonic flow at zero yaw angle to the principle panel length. For isotropic or orthotropic rectangular plates under an arbitrary nonzero yawed supersonic flow, then 36 or 6 x 6 natural modes are needed; for laminated anisotropic rectangular plates even at zero yaw angle, 36 or fewer natural modes are needed. To deal with such a large number of modes is computationally costly for flutter analysis, causing complexity and difficulty in designing controllers for flutter suppression. A thorough examination and understanding of the panel limit-cycle behavior leads to the use of aeroelastic modes for supersonic nonlinear panel flutter analysis. The system equations of motion are formulated first in structural node degrees of freedom. Aeroelastic modes are selected and determined, and the system equations is expressed in the aeroelastic modal coordinates. Limit-cycle amplitudes are then determined using numerical integration. Examples show that the number of modes could be greatly reduced by using aeroelastic modes. For determining limit-cycle oscillations of isotropic or anisotropic composite rectangular plates at zero or an arbitrary yawed flow angle, only two aeroelastic modes are needed; but six to seven aeroelastic modes are needed for designing controllers for flutter suppression.